Application of frequency converter in energy-saving transformation of double-station extrusion blow molding hollow molding machine

1introduction
In today's society, on the one hand, the economy is developing rapidly, and on the other hand, energy is increasingly scarce. The contradiction between development and energy is becoming more and more prominent. The problem of energy shortage has become an important issue in social development. It also puts forward more specific and stricter quantitative indicators. It is the responsibility of all companies to save energy. Therefore, energy-saving technologies and products in various industries have been continuously promoted and applied in recent years. Among them, frequency conversion energy-saving technology is the main energy-saving technology. One of the technologies has been widely used in plastics, cement, chemicals, central air-conditioning and other fields.
The plastics industry is one of the main industries, and its power consumption accounts for a large proportion of the industrial power consumption. With the increasingly fierce market competition, how to reduce production costs and improve product market competitiveness has become a concern of various plastics companies. In the production cost of various enterprises, plastic equipment accounts for a large part of the electricity consumption, and there is a large waste of electric energy in existing equipment. This article uses the GuozhaoGZSSeries of energy-saving appliances as an example, described the frequency conversion energy-saving technology in plastic equipment—The application of dual-station extrusion blow molding hollow molding machine in energy-saving transformation, and the necessity and feasibility of promoting this energy-saving technology are explained.

2Extrusion blow molding hollow molding machine working principle and composition
2.1working principle
Blow molding hollow molding machine is one of the main molding equipment for hollow products, mainly including extrusion blow molding hollow molding machine, injection blow molding hollow molding machine, stretch blow molding hollow molding machine and asymmetric blow molding hollow molding machine. Among them, the extrusion blow molding hollow molding machine uses the barrel heating of the extruder unit and the shearing action of the screw to plasticize the plastic. The rotating screw extrudes the plasticized and homogenized plastic through the die to form a tube blank. After the tube blank is clamped by the mold clamping device, the tube blank is cut by the cutter device, and pre-blowing is performed before cutting. The main purpose is to prevent the wall of the tube from sticking. The mold clamping blowing device seals the tube blank and blows in at the same time A certain pressure of air makes the parison close to the inner wall of the mold cavity. After cooling, the waste is removed, and the mold clamping device is separated to obtain the required hollow product.1Shown.

Figure1Extrusion blow molding hollow molding machine process flow

2.2Main composition
The extrusion blow molding hollow molding machine is mainly composed of an extruder, a die, a mold clamping device, a blowing device, a hydraulic transmission device, a heating and cooling control system, and an electrical control system. The outline drawing of the equipment is shown in the figure.2Shown.

Figure2Extrusion blow molding hollow molding machine equipment appearance diagram

Mechanical devices include mainly extrusion device (screw extruder), die head, mold moving mechanism, mold opening and closing mechanism, lifting mechanism, blowing device, blank electrothermal cutting device and die lifting device, etc.; the pneumatic device is mainly Used for cylinder work and blow molding of products, etc.; the cooling device mainly uses cooling water for cooling,Cooling water is mainly used for cooling of molds, barrels, blowing needles and other parts.
The electrical control system mainly consists of the extruder electric drive control system, the oil pump motor drive system control, the head and extruder heating and temperature control system, and the action program control system (PLC), human-machine interface and other components, the schematic diagram is shown in the figure3Shown.

Figure3Schematic diagram of electrical control of extrusion blow molding hollow molding machine

2.3Double station extrusion blow molding hollow molding machine
As mentioned above, the current blow molding hollow molding machine mainly includes extrusion blow molding hollow molding machine, injection blow molding hollow molding machine, stretch blow molding hollow molding machine and asymmetric blow molding hollow molding machine. Blow molding hollow molding machines are divided into single-station extrusion blow molding hollow molding machines, double-station extrusion blow molding hollow molding machines and multilayer extrusion blow molding hollow molding machines, of which double-station extrusion blow molding hollow molding machines The machine is mainly used for hollow products that have a long cooling time. It has two sets of mold clamping and mold shifting devices. While the product is cooling, another set of molds performs mold clamping and forming actions. Compared with the single-station model, the duplex The bit type machine makes full use of the cooling time when producing products, on the one hand, it can increase the output, on the other hand, it can also ensure the quality. application.

3Frequency conversion energy-saving transformation of double-station extrusion blow molding hollow molding machine
3.1Frequency conversion energy saving principle
The oil pump motor in the original system of the double-station extrusion blow molding blow molding machine always runs at a constant speed,When the pressure required by the process changes, it is adjusted by the proportional flow of the oil circuit system,Excess hydraulic oil is discharged back to the cylinder through the overflow valve,This also causes a large part of energy waste. From the pump load working characteristics, it can be seen that the flow rate of the pump is proportional to the speed, the head is squared with the speed, and the motor shaft power is squarely related to the speed.,As shown in the following formula:
Q2/Q1=N2/N1
H2/H1=(N2/N1)2
P2/P1=(N2/N1)3
among them:Q—flow;
N—Rotating speed;
H—Head.
As shown4When the flow is shown byQAReduce toQBDue to the characteristics of tube resistance, the operating point is determined byAPoint transferBPoint, the power consumed and0QBBHBThe area is proportional. If the frequency conversion control is adopted, the resistance characteristic of the tube remains unchanged, and the operating point is determined byAPoint transfer toCPoint, the power consumed and0QBCHCThe area is proportional, from the figure4It can be seen that the use of frequency conversion speed regulation and valve control is energy-saving, and the power of the motor is reduced with the decrease of the speed. If the speed of the oil pump motor can be adjusted in a timely manner according to the injection molding process, energy saving can be achieved.

Figure4Comparison of frequency conversion control and valve adjustment

At present, most three-phase asynchronous motors adopt frequency conversion speed regulation, and the motor synchronous speed formula is:
n=60(1-S)f/p；
among them:S—Slip rate
f—Power supply frequency
p—Number of pole pairs.
It is known from the above formula that the motor speed can be changed by changing the power frequency,Adjust the speed of the oil pump motor according to the process of the hollow blow molding machine,So as to minimize the return flow of the overflow valve,The output power of the hydraulic system matches the power required for production,This can achieve energy saving purposes,According to incomplete statistics, the power saving rate of the motor can reach25%~65%.